4.3: Functions and Applications of Alcohols

Hand Sanitizer

One common application for alcohol is in hand sanitizer. The presence of alcohol, usually ethanol or isopropanol, in hand sanitizers gives the sanitizers many of their useful properties. Perhaps the most useful property of hand sanitizers is the convenience of not having to dry off the hands after cleaning. This is because alcohol can evaporate quickly even though it exists as a liquid at room temperature. How quickly a substance evaporates is related to how strongly the molecules of the substance are attracted to each other and how much pressure is acting on the substance. If the molecules are strongly attracted to each other, the substance is more likely to be a solid or liquid because the molecules will be pulled close together. If the molecules are not strongly attracted to each other, the substance is more likely to exist in the gaseous state because the molecules only need a small amount of kinetic energy to pull away from each other. The hydroxyl group in alcohol has a slightly negative charge, so it would be loosely attracted to the more positively charged ends of other alcohol molecules (see the sections on intermolecular forces and boiling point in the “General Chemistry Background” chapter).

Alcohols are usually an ingredient in hand sanitizers like the one depicted here.

When the alcohol is inside the container, it is confined to a very small space. This results in a lot of pressure on the alcohol, causing it to stay in the liquid form. However, when the bottle is opened and the hand sanitizer is applied to the hands, there is much less pressure on the alcohol molecules. The attraction between the molecules is not strong enough to hold them in the liquid form, so the alcohol evaporates very quickly.

Alcohol is also an effective ingredient in hand sanitizers because it is able to effectively kill bacteria. The membranes of bacteria cells are made of a phospholipids bilayer, which is a type of fat. Because alcohols are soluble in fats, alcohol can bind to the membrane. When the alcohol molecules evaporate, they pull apart the membranes of the bacteria and cause the bacteria cells to die. Furthermore, alcohol denatures proteins in the bacteria. The polar hydroxyl group attracts compounds in the protein, causing them to bond to the alcohol. This prevents the proteins from forming correctly. Therefore, the amino acids cannot fold into polypeptides and are not able to carry out their designated purpose. Almost all cell functions depend on proteins, so when the proteins cannot form correctly, the cell is unable to function and dies.

Due to these unique properties of alcohols, scrubbing hands for thirty seconds with hand sanitizer has been deemed the equivalent to washing hands with soap in terms of killing harmful bacteria. For a more thorough cleaning, the best way to get rid of bacteria is to first wash the hands and then use hand sanitizer.

Test Your Understanding

The chemical acetone is used in nail polish remover, which quickly evaporates if left out. Describe the intermolecular forces between acetone molecules.

Why is water wet?

Based on your knowledge of dipole-dipole forces, which will evaporate first - ethylene (C2H4) or propanol (C3H7OH)?

Answers

Acetone molecules are held together very weakly because not very much energy is required to break the attraction between molecules that holds them in the liquid phase.

Water is a polar molecule, so water molecules exhibit strong dipole-dipole forces, which holds it in the liquid state at room temperature.

Ethylene will evaporate first because carbon atoms are not extremely electronegative, so each ethylene atom will not be polar and there will be no dipole-dipole forces. In fact, ethylene is a gas at room temperature. Proponal will have some dipole-dipole forces because the hydroxyl group will have a negative charge.

History of Ethanol in Beverages

In the past, alcohol was frequently consumed to avoid the spread of waterborne diseases. People noticed that those who consumed more wine than water contracted less diseases, but their knowledge of chemistry and biology was not enough to explain the reason why. Now it is known that water’s structure makes it ideal for dissolving many substances, including harmful ones. Because of this, water is often called “the universal solvent.” In comparison, alcohol molecules are larger and not as polar as water molecules. As a result, alcohol is not nearly as proficient in dissolving substances as water. Therefore, less harmful disease-causing substances are able to dissolve in alcohol than in water, making alcohol the “healthier” drink alternative when clean water is unavailable.

Even today, the issue of unclean water sources is still a prominent one. To learn more about the struggle many people face today to get clean water, visit this website:

Creation of Ethanol for Beverages

Perhaps the most well-known alcohol is ethanol, which is the type of alcohol found in alcoholic beverages. Other alcohols are considerably more poisonous and are not fit for human consumption. Ethanol is produced in a process called fermentation. In this process, yeast converts a molecule of glucose (C6H12O6), a type of sugar found in most plants, into two molecules of ethanol (C2H5OH) and two molecules of carbon dioxide (CO2). The chemical expression for this process is:

C6H12O6 --> 2C2H5OH + 2CO2

A variety of alcoholic beverages can be produced through the fermentation of sugars present in grapes, potatoes, wheat, and more. For example, grains are used to produce whiskey and beer, fruits (usually grapes) are used to produce wine, fruit juices are used to produce brandy, and sugarcane is used to produce rum.

LAB: Homemade Root Beer

The process of fermentation can be used to create not only alcoholic beverages but delicious soft drinks as well!

Materials

1 cup table sugar (cane sugar or sucrose)

1 tablespoon Root Beer Extract

1/4 tablespoon powdered baker's yeast (fresh and active)

cold fresh water

clean 2 liter plastic soft drink bottle with cap

funnel

Procedure

Use the funnel to add the sugar to the bottle.

Use the funnel to add the yeast on top of the sugar.

Shake to mix the yeast and sugar, then swirl it in the bottom so the surface of the mixture is concave (the surface should hollow inward like the inside of a bowl).

Use the funnel to add the root beer extract.

Fill the bottle halfway with pure water - the purer the water, the better. In the process, rinse off any extract that is stuck to the sides of the funnel and bottle. Swirl to dissolve all ingredients.

Once all ingredients are dissolved, fill the bottle to the top with water, leaving approximately 1 inch of space at the top.

Screw the cap securely onto the bottle to seal. Store the bottle at room temperature for 3-4 days, or until it becomes difficult to squeeze the bottle.

Refrigerate the bottle overnight. When opening, unscrew the cap slightly to release the pressure slowly.

Serve and enjoy!

Notes

Do not store the bottle in a warm place, especially after it begins to feel hard to squeeze. If it is left out in the heat, enough pressure can build up inside the bottle for it to explode.

Avoid glass bottles. If pressure causes the bottle to explode, glass shards could be dangerous.

The alcohol content in this beverage is between 0.35% and 0.5%, which is considered to be a negligible amount. A beer has 6% alcohol content, so in order to feel the same effects of consuming a 12-ounce beer, 1.5 gallons of root beer would have to be consumed. However, avoid this beverage if you cannot properly metabolize alcohols.

Effects of Ethanol as a Beverage

Blood Alcohol Content

The effects of ethanol when consumed include recklessness, clumsiness, slurred speech, delayed reflexes, and decreased inhibition. The chart below shows the common symptoms for different blood alcohol contents (BACs), which measures how many grams of ethanol are present for every 100 milliliters of blood.

The severity of the effects depends on the amount consumed as well as the weight, body type, and gender of the person. Because BAC is the grams of alcohol present divided by milliliters of blood, a heavier person will have a greater volume of blood and a lower BAC when consuming the same amount of alcohol as a smaller person. As a result, if two people consume the same amount of alcohol, the one who weighs less will be more affected by the alcohol. However, because alcohol is soluble in fats, a body with more fats will have a harder time of removing the alcohol. As women generally have more body fat than men, women generally become intoxicated more easily.

Alcohol and Neurotransmitter Receptors in the Brain

Scientists still do not know exactly why alcohol has the intoxicating effects that it is known for, but there are a few highly probable theories that would explain alcohol’s effect on humans. One widely accepted explanation is based on the attachment of alcohol to glutamate receptors. Glutamate is a non-essential amino acid, or a protein that can be made by the body. It acts as a neurotransmitter and is the most common stimulative neurotransmitter in the brain. The presence of glutamate increases the speed of neuron firing. Neurons are cells that exist throughout the body and work together to pick up, transmit, and interpret signals from outside the body. When glutamate is present, the signals are picked up, sent, and interpreted more quickly. As a result, glutamate is most often associated with learning and memory. For this reason, foods containing glutamate are usually considered as “brain foods.”

When alcohol travels through the digestive system, a small percentage of it is absorbed into the blood stream by the small intestine. The alcohol that is absorbed travels through the bloodstream and eventually reaches the brain. Upon reaching the brain, alcohol will bind to glutamate receptors, preventing glutamate from attaching to the receptors. Since the presence of glutamate increases the speed of neurons firing, the absence of glutamate slows the speed of neutrons firing. This causes the body to slow down and affects memory formation. The exact effects of this are determined by where exactly the alcohol molecules bind to the glutamate receptors. For example, the frontal lobe of the brain is used for judgment and reasoning. When ethanol binds to receptors in the frontal lobe, it can cause recklessness and decreased inhibition.

Scientists have also discovered that ethanol is able to attach to the GABA (gamma-aminobutyric acid) receptors. Unlike glutamate receptors, GABA receptors slow down brain activity. The attachment of alcohol to these receptors increases their activity, for reasons currently unknown to scientists. This slows down the body, causing the delayed reflexes and clumsiness often associated with ethanol consumption.

Excessive alcohol consumption can be very dangerous. The brain stem is a small but crucial portion of the brain that controls breathing, heartbeat, and other vital body functions. If ethanol molecules attach to receptors in the brain stem, these functions will slow down or shut down, resulting in coma or death.